1. Field of the Invention
The present invention relates to a reciprocating type compressor having a piston, and especially to a control valve thereof, such as a suction valve.
2. Description of Related Art
In a conventional reciprocating type compressor, a reed type valve is used as the suction valve. The reed valve is made of a thin metal plate, and is attached to the compressor as a cantilever-arm, with a free end covering the suction port. The reed valve is flexed by a pressure differential to rise slightly from the suction port, thereby opening the suction port. However, even when the suction port is so opened, the reed valve does not fully uncover and open the suction port. Therefore, when a reed valve is used as the suction valve, the suction port operates as a throttle, thereby reducing the suction efficiency. When the compressor is operating at a high rotational speed, this problem becomes significant.
For solving this problem, JP-A-5-202848 discloses a swash plate type compressor in which a rotary type valve is used as a suction valve instead of a reed valve. This rotary valve is cylindrically shaped, and the outer peripheral surface thereof includes a valve opening. The rotary valve is connected to a rotational shaft and rotates with the rotational shaft. Peripherally surrounding the rotational shaft and the rotary valve are a plurality of cylinders uniformly formed to be parallel to each other. Each cylinder includes a suction port opening on a wall surface thereof for selectively communicating with the valve opening of the rotary valve. The rotating rotary valve respectively opens and closes each cylinder suction port by respectively opening communication and closing communication between the rotary valve opening and each consecutive cylinder suction port as the rotary valve rotates. In such a compressor, a plurality of pistons installed in the cylinders are made to reciprocate inside the cylinders by a swash plate rotating with the rotational shaft, and compress fluid such as a refrigerant sucked into the cylinders.
However, the cylindrically shaped rotary valve is slidably rotationally installed inside a cylindrically shaped valve chamber formed in a cylinder block or housing, and rotates with an outer surface thereof frictionally rotationally sliding against the wall surface of the valve chamber. Thus, when the rotary valve rotates at a high speed, the relative velocity with respect to the wall surface increases, thereby requiring a sufficient supply of lubrication. Further, to obtain sufficient durability, it is necessary to use an expensive material for the cylinder block exhibiting high resistance to seizing and to provide a special surface coating on the friction surfaces, thereby increasing the manufacturing cost. Also, a clearance gap needs to be provided between the rotary valve and the wall surface due to machining limitations, thereby allowing the compressed fluid to leak through the gap and reduce compression efficiency. Further, if a large disc is used as the rotary valve instead of a cylinder, the rotating disc shaped rotary valve frictionally slides along the wall surface, thereby creating a large amount of friction force and reducing the compression efficiency.